Sprinkle with 1 tablespoon sugar; set aside. In small bowl,
combine cocoa, baking chocolate and boiling water. Stir until chocolate melts;
set aside. In another bowl combine flour, baking powder, baking soda and salt;
set aside. With mixer, beat 1 1/2 cups sugar and butter at medium speed until
well-blended, about 5 minutes. Add vanilla and egg whites, one at a time,
beating well after each addition. Add flour mixture to sugar mixture alternating
with buttermilk, beginning and ending with flour mixture. Stir in cocoa mixture.
Pour half of batter into pan, top with streusel and spoon remaining batter over
streusel. Bake for 1 hour, or until a tester comes out clean. Cool in pan on a
rack for 10 minutes, remove from pan and cool completely.

For Glaze:
Combine powdered sugar and butter in bowl. Add milk, and stir with whisk.
Drizzle over cake.